Liquid sampling apparatus for gas chromatography



Sept. 17, 1968 E. H. STOLL ETAL LIQUID SAMPLING APPARATUS FOR GAS CHROMATOGRAPHY Filed Feb. 28, 1966 Z 00 mm H W W w w a 2 m 0 4 5 6 2 3 2/4452 7 4 a 3 u 0 \\-\\\v \\v M 5 1 H a .x k TMH 5 6 w& 555

NELSON E. NUD/NG United States Patent 3,401,565 LIQUID SAMPLING APPARATUS FOR GAS CHROMATOGRAPHY Edward H. Stoll, Chicago, and Nelson E. Nuding, Brookfield, Ill., assignors to Armour and Company, Chicago,

111., a corporation of Delaware Filed Feb. 28, 1966, Ser. No. 530,732 7 Claims. (Cl. 73-422) This invention relates to gas chromatography and particularly to apparatus and a method for introducing samples from a fluid stream into gas chromatographic columns. More particularly, the invention pertains to a device for delivering a reproducible calibrated volume of a liquid sample into a carrier gas stream wherein the liquid is flash vaporized and flushed by the carrier gas stream into a gas chromatographic apparatus.

As a result of recent advances in gas chromatography, it has become highly desirable to be able to automatically analyze the contents of process streams by the technique of gas chromatography. Automated process operation may be achieved through the use of automated process analytical techniques coupled with automatic control of process operation. The automatic monitoring of process streams containing high boiling and chemically reactive materials, such as fatty acids and their derivatives, has not been satisfactorily achieved by the use of apparatus available prior to our invention. A review of the theory and the state of the art, particularly as applied to fatty acids and their derivatives, may be found in L. D. Metcalfe, Gas Chromatography in the Fat and Oil Industry, in The Journal of the American Oil Chemists Society, volume 41, No. 5, May 1964, page 4.

Automatic transfer of a sample directly from a liquid process stream into a gas chromatography column presents many problems including precise sample metering, contamination, and achievement of flash vaporization of the liquid sample. The major problems associated with automatic sampling of process streams of high boiling materials in the past have been the transfer of a reproducible precise sample from a liquid process stream which is maintained at a temperature in the order of 80 C. into a zone for flash vaporization which requires temperatures of over 300 C. and thence into the gas chromatography column. Some prior devices have attempted to sample at higher temperatures, but this required maintaining the sample takes under high pressure to retain the samples in a liquid state for precise metering and transporting to the vaporization zone. Transporting the metered liquid sample to the point where it is to be vaporized is a fundamental problem in process chromatography. If the path is too long, interfacial contamination from the previous sample will become objectionable; if it is too short, the volatile materials vaporize in the sample lines, excessive heat conduction causing vapor-lock and erratic sample metering. Other prior methods have attempted'to adopt various pipet assemblies for sample metering, but these have been generally unsatisfactory due to the difficulty in automating the pipet operation and due to the difficulty in obtaining complete removal of the sample from the capillary chamber of the pipet.

It is an object of this invention to provide apparatus and a method for the transfer of a reproducible calibrated volume from a liquid process stream to a position in a carrier gas stream wherein the liquid is flash vaporized and flushed by the carrier gas stream into a gas chromatography column.

It is a further object of this invention to provide apparatus and a method satisfactory for precise automatic sampling of a liquid process stream containing high boiling and reactive materials, flash vaporization of the samice ple, and flushing such vaporized sample into a gas chromatographic apparatus.

It is still another object of this invention to provide apparatus and a method for the automated reproducible sampling of liquid process streams containing fatty acids having chain lengths of up to thirty carbon atoms and transfer of the sample to a flash vaporization zone without the pressurization of sample lines for the purpose of maintaining the sample in the liquid phase.

Further details and advantages of this invention will be described in connection with the accompanyng drawings illustrating preferred embodiments of this invention and wherein:

FIGURE 1 is a cross section of a preferred embodiment of an automated liquid sampling apparatus for gas chromatography according to this invention; and

FIGURE 2 is an enlarged section showing the sample containment portion of the apparatus shown in FIG- URE 1.

Referring to FIGURE 1 in the drawings, the apparatus comprises sample chamber 11, and having through passages 12 for influent liquid and 13 for efiluent liquid, and having upper opening 14 and lower opening 15 arranged in opposed position to each other. It is preferred that influent passage 12 and effluent passage 13 be located in sample block 10 diagonally from each other so as to provide for eflicient flushing of the sample chamber by the sample stream to avoid stagnant volumes within the sample chamber which would result in the sample being non-representative of the actual contents of the sample stream. Sample chamber block 10 may be constructed of any suitable material, stainless steel being preferred due to its corrosion resistance and ease of cleaning. Rod 20 passes through upper and lower opposed openings 14 and 15 respectively of sample block 10, and has depression 21 for containment of a calibrated volume of liquid from the sample stream. Rod 20 may be solid for its entire length or, alternatively, may be hollow for portions of its length away from depression 21. Rod 20 may be constructed of any suitable material, stainless steel being preferred due to its high rigidity and strength.

Second tube 30, adjacent to and aligned with lower opening 14, permits passage of rod 20 in such a manner that the liquid sample in depression 21 is accurately metered by passage of depression 21 through tube 30. This may be accomplished by liner 31 having inner surface 37 fitting snuggly about rod 20 permitting free passage of rod 30, but at the same time maintaining a snug -fit so that the volume of liquid sample contained in depression 21 is uniform in each sampling cycle. Maintaining such snug fit is difficult due to the lower end of the tube being located in a heated zone while the upper end of the tube is adjacent to sample chamber block 10 which as heretofore mentioned is maintained at a lower temperature. The required fit has been successfully achieved by utilizing Teflon for liner 31 and restraining liner 31 from alteration of shape by containing it within tube 32.

The upper end 23 of rod 20 is attached to an actuating means for positioning rod 20 in an upper position whereby depression 21 resides in sample chamber 11 and for moving rod 20 downwardly causing depression 21 to move through tube 30 to a lower position entirely below tube 30 while retaining a calibrated volume of liquid in depression 21 and for returning rod 20 to said upper position. Suitable actuating means may be hand, mechanically, pneumatically or electrically operated. An appropriate automatic actuating means shown in FIGURE 1 comprise generally cylinder 40 having cylinder line 41 within cylinder 42, top 43 and bottom 44. Cylinder liner 41 is preferably fabricated from Teflon to provide a low friction surface. Piston 60 is attached to the upper end 23 of rod 20 permitting movement freely through cylinder liner 41. Piston 60 is forced downwardly through cylinder liner 41 by the ingress of air through upper opening 49 with the concurrent egress of air through lower opening 48 to a position wherein lower piston surface 63 rests against lower piston stop 52 which is held by lower piston stop shoulder 51. Conversely, ingress of air at lower air opening 48 with the concurrent egress of air through upper opening 49 moves piston 60 carrying rod 20 to said upper position maintained by upper piston stop 50. Air tightness is achieved by piston seals 61, lower liner seal 53 and upper liner seal 54, which may be O-rings of Viton A.

Second tube 70 is so positioned adjacent to tube 30 that movement of rod 20 to said lower position establishes contact of rod 20 with second tube 70. Second tube 76 has entrance 71 and exit 72 permitting flow of carrier gas from carrier gas passage 81 through second tube 70 into the chromatographic column. Second tube 70 is heated by any appropriate means so as to cause transference from inner wall 73 to rod 20 in contact therewith sufiicient to cause flash vaporization of the calibrated volume into the carrier gas stream flowing through said second tube and thence into the gas chromatographic column. Contact for heat conductance from inner wall 73 of tube 70 to the lower end 22 of rod 20 may be achieved in several ways. For example, one side of the inner wall 73 may be oblique to the line of travel of rod 20 so that lower end 22 establishes firm contact therewith when rod 20 is in said lower position. Likewise, firm contact may be established by interior wall 73 forming a tapered elliptical cross-section form such that lower end 22 fits tightly within the short axis of the ellipse while free passage of carrier gas is permitted between lower end 22 and inner wall 73 on the long axis of the ellipse. Obviously, other physical arrangements would be possible and would clearly fall with in the invention.

Second tube 70 is maintained at an elevated temperature sufiicient to transmit heat to lower end 22 of rod 20 to cause flash vaporization of the calibrated volume in depression 21. In the case of fatty acids and their derivatives such as amines, the second tube should be maintained at from about 250 to 330 C. These temperatures have permitted analysis of fatty acids having a chain length of up to about 30 carbon atoms. FIGURE 1 shows a suitable embodiment for maintaining second tube 70 at an elevated temperature by surrounding second tube 70 with heater block 80 in which are mounted electrical resistance heaters 84 sufiicient to maintain the required temperatures. Such a heater block has the additional advantage of raising the carrier gas to an elevated temperature by passing it through passage 81 prior to introduction into second tube 70.

As previously stated, one of the difficulties in obtaining an effective injector system from a liquid stream into a gas chromatographic column is the desirability of operating the sample chamber at a sufficiently low temperature to maintain the sample in a liquid phase while obtaining sufiicient heat in the sample vaporization zone to flash vaporize the sample. The desirable temperature differential may be enhanced by the addition of cooling coils 90 between the sample vaporization zone and the sample chamber. Alternatively, materials may be selected affording sufliciently low heat conductance as well as various air-cooled structures.

Referring to FIGURE 2 in the drawings, the portion of rod 20 having depression 21 is shown enlarged. It is preferred that the depression 21 be a concave depression of semi-elliptical shape located on one side of the rod in a portion of the rod which is solid. It is important that the surface 24 of concave depression 21 be shallow so that liquid may not be held in the depression by capillary action.

In operation, rod 20 is positioned so that depression 21 is within sample chamber 11 through which a by-pass of the process stream is flowing. This position is maintained for a suflicient period of time to permit thorough washing of depression 21 with the liquid of the process stream. Injector rod 20 is then carried downwardly through the snug fitting tube 30 whereby the sample residing in depression 21 is automatically and precisely metered. The metered sample within depression 21 then emerges from the lower end of the tube 30 into an environment of carrier gas flowing through second tube 70 into the chromatographic column. The lower end 22 of rod 20 comes into contact with interior wall 73 of second tube 70 conducting heat therefrom through rod 20 to depression 21 sufficient to cause flash vaporization of the metered sample therein. Flash vaporization of the sample may be further enhanced by warming the carrier gas prior to its contact with the sample. The vaporized sample is then carried by the carrier gas stream into a gas chromatographic column for analysis.

Any suitable gas chromatographic analyzing apparatus may be utilized to perform analysis of the sample introduced into the gas chromatographic column by the apparatus of this invention. Such instruments are well known to those skilled in the art. Further, any suitable carrier gas, such as helium, may be utilized.

From the above description, it will be apparent that the objects of the invention have been attained and, although the invention has been described with reference to a preferred embodiment thereof, it is to be understood that this is by way of illustration only. It is readily seen that modifications and variations may be made in the apparatus by those skilled in the art in view of our description without departing from the spirit of the invention.

We claim:

1. Apparatus for transferring a calibrated volume from a liquid stream into a carrier gas stream for introduction into a gas chromatographic column which comprises a sample chamber block having a cavity forming the sample chamber, said block having through passages for influent and etfiuent liquid and upper and lower opposed openings; a rod having a depression for containment of said calibrated volume, said rod passing through said upper and lower opposed openings; a tube adjacent to and aligned with said lower opening; actuating means for positioning said rod in an upper position whereby said depression resides in said sample chamber and for moving said rod downwardly causing said depression to move through said tube to a lower position entirely below said tube While retaining a calibrated volume of liquid in said depression and for returning said rod to said upper position; a second tube so positioned adjacent said tube that movement of said rod to said lower position establishes contact of said rod with said second tube, said second tube having an entrance and an exit permitting flow of said carrier gas through said second tube into the chromatographic column; and means for heating said rod sufficient to cause flash vaporization of the calibrated volume into the carrier gas stream flowing through said second tube and thence into the gas chromatographic column.

2. The apparatus of claim 1 wherein said depression is a concave depression on one side of said rod.

3. The apparatus of claim 2 wherein said depression has semi-elliptical shape.

4. The apparatus of claim 1 wherein said second tube has an inner wall oblique to the line of travel of said rod.

5. The apparatus of claim 1 wherein said passages for influent and eflluent liquid are located diagonally from each other in said sample chamber block.

6. The apparatus of claim 1 wherein said tube contains a liner having an inner surface fitting snugly about said rod so that the volume of liquid sample contained in saiddepression is uniform in each sampling cycle.

7. The apparatus of claim 1 wherein said actuating means is pneumatically operated.

(References on following page) 5 6 References Cited FOREIGN PATENTS UNITED STATES PATENTS 1,190,697 /196 G y- 2,991,647 7 51 Harris 73 23 DAVID SCHONBERG, Primary Examiner.

3,100,984 8/ 1963 Martin. 5 S. CLEMENT SWISHER, Assistant Examiner. 

1. APPARATUS FOR TRANSFERRING A CALIBRATED VOLUME FROM A LIQUID STREAM INTO A CARRIER GAS STREAM FOR INTRODUCTION INTO A GAS CHROMATOGRAPHIC COLUMN WHICH COMPRISES A SAMPLE CHAMBER BLOCK HAVING A CAVITY FORMING THE SAMPLE CHAMBER, SAID BLOCK HAVING THROUGH PASSAGES FOR INFLUENT AND EFFLUENT LIQUID AND UPPER AND LOWER OPPOSED OPENINGS; A ROD HAVING A DEPRESSION FOR CONTAINMENT JOF SAID CALIBRATED VOLUME, SAID ROD PASSING THROUGH SAID UPPER AND LOWER OPPOSED OPENINGS; A TUBE ADJACENT TO AND ALIGNED WITH SAID LOWER OPENING; ACTUATING MEANS FOR POSITIONING SAID ROD IN AN UPPER POSITION WHEREBY SAID DEPRESSION RESIDES IN SAID SAMPLE CHAMBER AND FOR MOVING SAID ROD DOWNWARDLY CAUSING SAID DEPRESSION TO MOVE THROUGH SAID 